Method for producing iron base sintered alloys containing copper

ABSTRACT

THIS INVENTION RELATES TO SINTERED METAL ALLOYS SUCH AS IRON BASE ALLOYS CONTAINING COPPER HAVING SIGNIFICANTLY IMPROVED TOUGHNESS CHARACTERISTICS, AND A METHOD FOR MAKING SUCH ALLOYS. A NOVEL STRUCTURE IS PRODUCED CHARACTERIZED BY A NON-HOMOGENEOUS CONCENTRATION OF COPPER SOLID SOLUTION WITHIN THE INDIVIDUAL BASE METAL PARTICLES COMPRISING SAID SINTERED STRUCTURE. SUCH A STRUCTURE IS OBTAINED BY CONTROLLING THE TIME-TEMPERATURE PARAMETERS DURING THE SINTERING AND DIFFUSING STEPS THEREOF. FOR EXAMPLE, SINTERING IS PERFORMED AT A TEMPERATURE LESS THAN THE MELTING POINT OF COPPER; THE DIFFUSION AT A TEMPERATURE RANGING FROM THE MELTING POINT OF COPPER TO LESS THAN THE MELTING POINT OF THE IRON BASE MATERIAL.

Juiy 4, 1972 TAKASHI KIMURA ETAL 3,74,47

METHOD FOR PRODUCING IRON BASE SINTERED ALLOYS CONTAINING COPPER Filed June 6, 1969 5 Sheets-Sheet l INVENTORS 734K SH AIMMQH, 42034 MAM/MA, f/IEOSH/ HflMfl/WO To,

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METHOD FOR PRODUCING IRON BASE SINTERED ALLOYS CONTAINING COPPER 5 Sheets-Sheet" 2 Flied June 6, 1969 F B G. 8

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July 4, 1972 METHOD FOR PRODUCING IRON BASE SINTERED ALLOYS CONTAINING COPPER 5 Sheets-Sheet 5 Filed June 6, 1969 FEEGJO FIGH BY A W m Wu,

ATTORNEYS July 4, 1972 TAKASHI KIMURA ETAL 3,674,42

METHOD FOR PRODUCING IRON BASE SINI'ERED ALLOYS CONTAINING COPPER Filed June 6, 1969 5 Sheets-Sheet INVENTORS. TAKAT 8H! K/MUE A, AZUS4 MA u/M A, H/EOSH/ boa/144M07 you/ 4 WA No,

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ATTORNEYS.

4, 1972 TAKASHI KIMURA ETAL 3,74A

METHOD FOR PRQDUUING IRON BASE SINTERED ALLOYS CONTAINING COPPER.

Filed June 6, 1969 Sheets-Sheet s F1617 F161 (Kg/mm g/m 3O 1 I I" 64 l I l 2 0 15 3O 5 (min) }2 (min) INVENTORa TflkfflS/f/ K YM (IE4, 424/614 Mflu/Mfi, /neosfi/ HA/WAMOTQ YOz/l fiVfl/VO,

ATTORNEYS 3,674,472 METHOD FOR PRODUCING IRON BASE SINTERED ALLOYS CONTAINING COPPER Takashi Kimura, Nagoya-shi, Azusa Majima, Showa-ku, and Hiroshi Hamamoto and Yoji Awano, Nagoya-shi, Japan, assignors to Kabushiki Kaisha Toyota Chuo Kenkyusho, Nogoya-shi, Japan Filed June 6, 1969, Ser. No. 831,088 Claims priority, application Japan, June 18, 1968, 43/ 42,089 Int. Cl. BZZE 3/16 US. Cl. 75-421 3 Claims ABSTRACT OF THE DISCLOSURE This invention relates to sintered metal alloys such as iron base alloys containing copper having significantly improved toughness characteristics, and a method for making such alloys. A novel structure is produced characterized by a non-homogeneous concentration of copper solid solution within the individual base metal particles comprising said sintered structure. Such a structure is obtained by controlling the time-temperature parameters during the sintering and diffusing steps thereof. For example, sintering is performed at a temperature less than the melting point of copper; the diffusion at a temperature ranging from the melting point of copper to less than the melting point of the iron base material.

This invention relates generally to improved sintered alloys, and particularly to iron base sintered alloys containing copper having improved toughness characteristics, as formed, along with a method for making such alloys.

In the powder metallurgical art, iron, brass, tungsten, molybdenum, or other metal powders of flour-like consistency may be admixed with other powdery materials, such as copper, cobalt, silver, etc.; compressed in a mold to form green compacts; and thereafter heated at a temperature below the melting point of the compact materials to form a sintered product. It is well-known that such sintered products have poor toughness properties, i.e., they are frangible and have poor elongation or ductility properties.

Numerous attempts to improve the properties of the aforementioned sintered compacts have been made, some of which involve complex and expensive equipment, such as high pressure, high temperature 'extruders, for working the as-formed frangible material. Another technique practiced today seeks to reduce porosity of the compact by increasing its density and thereby minimize the points of weakness. For this purpose, metal powders having excellent compressibility characteristics are selected and compressed; significantly larger pressures are employed to force the particles closer together. Further, the sintering time is prolonged and/or the sintering temperature is raised. Although this method is generally satisfactory when a single metal powder is processed as, for example, iron, it is not satisfactory when multi-component systems, including sintered iron alloys containing copper, are to be produced. Such sintered alloy products when produced by the aforesaid conventional methods are characterized by high strength, but with notably poor elongation or toughness properties.

Extensive investigations were, therefore, undertaken to determine the relevant factors contributing to the physical properties of as-formed sintered iron alloys and especially -sintered iron alloys containing copper. By isolating and analyzing the various factors contributing to such Patented July 4, 1972 low elongation, it was hoped a new approach for producing sintered alloys having outstanding toughness with concomitant high strength properties would result. Such an improved material would have general use in automotive applications including automobile parts, while the method employed would have the advantages inherent in powder metallurgical processes, as for example, low cost and high volume.

Various metallographic structures of sintered iron base alloys were formed under controlled conditions and subsequently analyzed and tested, as will be described hereinafter in greater detail. Surprisingly, it was discovered that an important, if not critical, factor contributing to toughness, or lack of same, is the particular distribution of dissolved alloying metal e.g., copper within the base metal matrix.

In the conventional method for producing such sintered materials, the first steps of sintering and diffusing or infiltrating copper therein are generally carried out simultaneously at a temperature above the melting point of copper and the structure formed by such method is generally homogeneous, that is, a copper solid solution is uniformly distributed, or dissolved, within the iron particles. Further, it was discovered that when an alloying element such as copper is purposely prevented from being distributed uniformly within the base metal, but is, instead, concentrated non-uniformly Within the base metal particles adjacent the boundaries thereof, a significant improvement in the toughness of such a product is thereby obtained. Thus, a significant break-through in producing a sintered metal alloy with superior toughness charac teristics was achieved.

By carefully regulating the time-temperature parameters in the sintering and diffusing steps, the tensile strength-elongation properties are tailered and controlled. Thus, using the present invention, a non-homogeneous, or heterogeneous, structure with improved toughness properties is obtained 'when an iron-copper compact is first sintered at a temperature below the melting point of copper (1083 C.), and then heated for a shortened period of time at a temperature above the melting point of copper, whereupon molten copper diffuses as a solid solution into the iron base metal matrix and concentrates along the inner boundaries thereof. This is in contrast to conventional methods which use higher temperatures, e.g., above 1083 C., for longer periods of time, thereby producing a homogeneous structure.

As used throughout this specification the term toughness is generally meant to include the strength of the material plus its ability to be deformed permanently without rupturing. Although toughness is not generally measured directly, the elongation of the material is an indirect measure of this property.

A primary object of the present invention is the provision of an easy-to-produce sintered alloy from compacted metal powders, with improved toughness characteristics.

Another object of the present invention is the provision of a sintered alloy having a higher concentration of ditfusable metal distributed within the base metal network, or matrix, along the boundaries thereof.

Still another object of the present invention is the provision of a sintered iron base alloy containing copper wherein the copper is heterogeneously distributed within the network of the iron base metal matrix.

A further object of the present invention is the provision of methods for producing a sintered metal alloy as described above.

Yet another object of the present invention is the provision of relatively simple and inexpensive methods of producing iron base sintered alloys containing copper having significantly improved toughness characteristics over those produced using conventional methods.

Numerous other objects and advantages of this invention will be apparent from the following description and accompanying drawings.

Referring to the drawings:

FIG. 1 is an enlarged pictorial representation of a compact structure formed from compressed iron and copper powders admixed.

FIG. 2 is an enlarged pictorial representation of the compact of FIG. 1, after sintering in accordance with conventional methods.

FIG. 3 is a diagram showing the microscopic observation of the structure of an iron-copper sintered alloy formed in accordance with the conventional method.

FIG. 4 is a line analysis graph of the iron-copper sintered alloy of FIG. 3 obtained from an electron probe microanalyzer, or EPMA, wherein the ordinate represents the concentration of copper in weight percent distributed within the structure, and the abscissa is the distance in microns ,u. across the structure.

FIG. 5 is an enlarged pictorial representation of a compact structure formed of compressed iron powder alone.

FIG. 6 is an enlarged pictorial representation showing the compact of FIG. 5 sintered and at the same time infiltrated with molten copper in accordance with the conventional infiltration methods. 1.;

FIG. 7 is a diagram showing the microscopic observation of the iron-copper sintered alloy structure of FIG. 6.

FIG. 8 is a line analysis graph of the structure of the iron-copper sintered alloy of FIG. 7 obtained from an electron probe microana-lyzer, wherein the ordinate and abscissa are as in FIG. 4.

FIG. 9 is an enlarged pictorial representation of a sintered structure of previously admixed iron and copper particles as produced in accordance with this invention.

FIG. 10 is an enlarged pictorial representation of the sintered structure of FIG. 9 after controlled diffusion is carried out in accordance with this invention.

FIG. 11 is a diagram showing the microscopic observation of the iron-copper sintered alloy structure of FIG. 10.

FIG. 12 is a line analysis graph of the structure of FIG. 11 obtained from an electron probe microanalyzer, wherein the ordinate and abscissa are as in FIG. 4.

FIG. 13 is an enlarged pictorial representation of" a sintered structure formed from a compact of iron powder and then sintered in accordance with the present invention.

FIG. 14 is an enlarged pictorial representation of the sintered structure of FIG. 13 after infiltration by molten copper in accordance with the present invention.

FIG. 15 is a diagram showing the microscopic observation of the infiltrated iron-copper sintered alloy of FIG. 14.

FIG. 16 is a line analysis graph of the structure of FIG. 15 obtained from an electron probe microanalyzer, wherein the ordinate and abscissa are as in FIG. 4.

FIG. 17 illustrates, in graph form, the effect of heating time (abscissa) on the tensile strength (S and elongation (1 for sintered iron-copper alloys produced from admixed powders of iron and copper and processed in accordance with this invention.

FIG. 18 illustrates, in graph form, the effect of heating time (abscissa) on the tensile strength (S and elongation (1 for sintered alloys produced by infiltrating molten copper into the sintered iron compact in accordance with the present invention.

Broadly, the present invention is directed to improved sintered alloys, particularly those alloys comprising an iron base network containing copper, and methods for producing the same.

conventionally, sintered metal products are made by filling a durable metal mold with fine metal powder; thereafter compressing the powder under high pressure- 4 fro 5 to 8 t./cm. -to produce a compact which is heat treated at elevated temperatures to form a sintered product.

The present invention uses conventional techniques in forming the pre-sintered compact, but departs therefrom in the sintering and diffusing steps following. The thrust of this invention, therefore, lies in the heat treatment of iron base compacts, i.e., controlled sintering of the compact and diffusing an alloying metal, preferably copper, therein to obtain a non-homogeneous structure wherein a solid solution of copper is concentrated along the boundaries of the sintered iron particle network to form a material having improved toughness characteristics.

Three general approaches were successfully used in producing a non-homogeneous sintered alloy of the present invention. One approach involves a sintered iron base material infiltrated by molten copper. Here, a compact of iron base metal powder is first compacted and sintered at a temperature range from about its initial sintering point, or 700 C., to below the melting point of iron to produce a porous network of partially coalesced or merged iron base material. Thereafter, the sintered product is heated at a temperature ranging from about the melting point of copper, or 1083 C., to a temperature below the melting point of iron, or 15 39 C., in the presence of molten copper. A prefer-able range is from about 1100 C. to 1500 C. The heat treatment is stopped before the copper is uniformly diffused within the iron base material to form a homogeneous structure. Stated another way, by controlling the heating time molten copper is permitted to diffuse into the iron base material, as a solid solution, thereby concentrating in the boundary areas of the sintered metal particles to produce a heterogeneous structure having increased toughness properties.

In a second approach, an admixture of iron and copper powders is placed in a metal mold, compressed to form a compact and thereafter sintered, first, at a temperature of about 900 C., and then at a higher temperature of about 1100 C. to produce a non-homogeneously diffused structure containing concentrated copper solid solution therein.

The initial compact is produced using a combination of various metallic and non-metallic powders such as nickel or carbon power.

The resulting meallographic structures produced in accordance with this invention are illustrated in FIGS. 10, ll, 14 and 15 of the accompanying drawings with the contrasting conventional structures being shown in FIGS. 1, 2, 3, 6 and 7.

Referring now to the drawings in detail, a typical compressed metal powder structure, or compact, is shown 1n FIG. 1 wherein the numeral 1 is illustrative of a copper particle in contact with surrounding iron particles 2; the compact being formed of an admixture of iron powder and up to 8% copper powder, by Weight. In a conventional process for producing an iron-copper sintered alloy the compact of FIG. 1 is heated at a temperature above the melting point of copper, as for example, at 1150 C. for an extended period of time, such as minutes, whereby the copper melts, diffusing into the iron particles 2, forming a homogeneous structure of a uniformly dissolved solid solution of copper therein.

In FIG. 2 sintered iron particles 21 are shown as partially merged, or coalesced, with one another including a bridge or neck portion in between the sintered particles 21. The hatch lines represent a substantially uniform concentration of dissolved copper within the base metal matrix.

In FIG. 3 a microscopic observation, shown at 400x magnification, of a conventionally formed sintered metal alloy structure comprising iron particles 21 with uniformly distributed copper solid solution dissolved therein to form a homogeneous structure; the structure being formed from admixed iron and copper powders, compressed and thereafter sintered at a temperature exceeding the melting point of copper. After diffusion of the copper particles, the structure is porous having voids 3 formed therein in place of the copper particles. Analytical confirmation of the conventionally obtained homogeneous structure is shown in FIG. 4 which was obtained with an electron probe microanalyzer by quantitative measurements of the composition at different points within the particle structure. Thus, in FIG. 4, the sintered structure was confirmed to have a substantially uniform distribution of copper solid solution throughout the iron-copper sintered alloy material. The concentration of this copper solid solution was measured at approximately 2% by weight.

Similar homogeneous structures were obtained from a conventional infiltration process; an iron-copper sintered alloy produced by subjecting a sintered iron powder compact to molten copper for an extended per1od of time, e.g., about 60 minutes. The copper infiltrated the porous structure filling each pore 3 and also coating the iron particles 2, as shown in FIG. 5. During the extended heating period molten copper diffused into the iron particle matrix and uniformly dissolved therein as a homogeneous structure of a copper solid solution. Simultaneously, the iron particles partially dissolved into the copper occupying pore 3'. The resulting structure, shown in FIG. 6 and FIG. 7, at 400x magnification, is characterized by individual iron particles 21 having a uniformly distributed solid solution of copper dissolved therein and bridged w th copper 12 having iron partially dissolved therein. A llne analysis obtained from an electron probe microanalyzer, and shown in FIG. 8, clearly confirmed the formation of a solid solution of copper dissolved uniformly throughout the iron particles to give a homogeneous structure, said copper measuring about 8% by weight and upper portions of the graph correspond to the pores between iron particles filled with copper. The lower portions P which correspond to the iron articles are the same level and they show that copper is infiltrated uniformly in the iron particles.

Thus, it is readily seen that the iron-copper sintered alloys produced in accordance with two conventional methods described above, produce a structure with a common characteristic, that is, a homogeneous distribution of copper solid solution uniformly dissolved within the iron particles. Physically, such a homogeneous structure is frangible and has poor toughness characteristics.

Under the present invention an admixture comprising iron powder and copper powder is compacted and sintered at a temperature preferably between the sintering point of the base metal and the melting point of copper, then heated at a temperature above the melting point of copper, preferably around 1100 C. After the sintering step is completed, the structure of FIG. 9 is obtained. Iron particles 2 are partially coalesced, forming bridges or neck portions n. Thus, sintered networks of partially coalesced iron particles 2 surround undissolved solid copper particles 1 whereupon the temperature is raised sufficiently to melt the copper particles, but not the iron. By keeping the heating time less than 60 minutes and preferably from 4 to 30 minutes, a non-homogeneous structure, as illustrated in FIG. 10, is formed wherein copper solid solution is concentrated within the boundary areas of the iron matrix, shown at 22. Under microscopic observation, at 400x magnification, the iron-copper sintered alloy produced by sintering and heat treatment was found to have very little, if any, copper in portion 20, as shown in FIG. 11, even though portion 22 was considerably enriched with dissolved copper. A porous structure having voids 3 Was formed after the dissolution of the copper into the iron base matrix.

A line analysis obtained from an electron probe microanalyzer, and shown in FIG. 12, clearly confirmed the formation of a non-uniform distribution of copper solid solution throughout the iron base sintered alloy forming a heterogeneous structure. The level of the bottom portions of the graph which correspond to iron particles have considerable variance according to the variance of infiltrated copper in iron particles.

Using the process of this invention on infiltrated sintered materials similar non-homogeneous structures are obtained. For example, a compact of iron powder is formed and sintered at 1100 C., as illustrated in FIG. 13, wherein iron particles 2 partially coalesce with each other to form a bridge or neck portion 11. The porous structure 3 receives molten copper at a temperature of approximately 1100 C. for a relatively short time, ranging from 4 to 30 minutes. Due to the shortened heating period, diffused copper solid solution is prevented from being unlformly distributed throughout the iron base matrix. Thus, a non-homogeneous structure is formed. Simultaneously, the iron particles are partially dissolved into the copper occupying pore 3. The resultant structure shown in FIG. 14, and FIG. 15, at 400 magnification, is characterized as a heterogeneous structure of partially merged iron particles 2 with copper solid solution concentrated along the inner boundary areas therein, as at 22, and with iron dissolved in the copper-containing pore structure '12. A relatively copper-free portion is shown at 20.

A line analysis obtained from an electron probe microanalyzer, and shown in FIG. 16, clearly confirmed the heterogeneous structure, as mentioned above. Wide variances in the concentration of copper solid solution were noted; ranging from almost 0 to 8%, by weight, as shown by P.

The effect of heating time on the physical properties of the sintered alloy produced in accordance with the teachings of this invention is shown in FIGS. 17 and 18. Curves S 1 represent in FIG. 17 tensile strength and elongation, respectively, of specimens prepared from a sintered compact comprising admixed iron-2% copper. The compact was compressed under 5 t./c:m. and sintered at 900 C. for 60 minutes, and thereafter heated at 1100 C. for a predetermined period of time.

As shown in FIG. 17, as the heating time increases from about 0 minutes to 16 minutes the tensile strength sharply increases, after which it levels olf to substantially 26 kg./mm. The elongation 1 however, reaches its maximum value of approximately 10% within the first 4 minutes of heating, gradually declining thereafter. Between 4 minutes and 30 minutes elongation dropped from about 10% to 6%. Using these curves it is, therefore, possible to obtain a desirable combination of high tensile strength and high elongation in sintered metal alloys when such alloys are heated at a controlled temperature for periods less than 60 minutes and preferably, from 4 minutes to 30 minutes. At approximately 16 minutes a sintered product having outstanding toughness characteristics is obtained. The effect of heating time on test specimens which were obtained from materials formed from iron powder compressed under a pressure of 5 t./cm. sintered at 1100 C. for 60 minutes and then infiltrated with molten copper at 1100 C. for a predetermined period of time is shown in FIG. 18. The specimens prepared therefrom were tested for tensile strength and elongation, curves S and 1 representing these properties, respectively. As shown, the tensile strength sharply increases within the first 60 minutes, or so, to a value of about 52 kg./mm. and thereafter levels off to a value of about 60 kg./mm. The elongation, however, falls rapidly within the first 60 minutes from values exceeding 22% to those of about 8%, thereafter moderating to about 3%. Again, a desirable combination of properties may be obtained for an infiltrated sintered alloy product when the heating time is kept less than 60 minutes and preferably, from 4 to 30 minutes.

From the graphs shown in FIGS. 17 and 18, a range of optimum heating time may be selected. However, it should be understood that the temperature range is critical to obtaining the desired structure. For purposes of illustration, a heating temperature of 1100 C. was selected. However, other temperatures ranging from about the melting point of copper, to below the melting point of iron preferably within the range from 1100 C. to 1500" C., may be chosen. The position of the tensile strength and elongation curves will shift depending upon the heating temperature. For example, at a temperature above 1100 C. diffusion will be accelerated, therefore, a shortened time period would be used to obtain equivalent results. Conversely, a lower temperature would require increased heating time.

The specimens tested were produced from an ironcopper sintered product. However, other sintered alloy products including metals and non-metals may also be used. For example, nickel, and carbon powders were additionally admixed with iron powder and processed in accordance with the present invention.

Although not wishing to be bound by any particular theory as to the precise mechanism involved in producing the significantly higher toughness characteristics, it is thought that the controlled heat treatment of the present invention and the non-homogeneous concentration of diffused copper avoids damage to the constricted neck portion n of said sintered structure and contributes to the strength of said portion.

Having described the basic aspects of the present invention, the following examples are given to illustrate the specific embodiments thereof. It should be understood that the examples shown are merely preferred embodiments and that various modifications in both the method and materials are contemplated therefor.

It should also be understood that the compacts used in preparing the specimens shown in the following examples were prepared from commercially available metal powder suitable for sintering purposes. The powder was compacted in metal molds at t./cm. in accordance with the standards set forth by the Japan Powder Metallurgical Association for standard tensile strength specimen preparation. Subsequent heat treatment of the compact was carried out in accordance with this invention in a twozone furnace with hydrogen atomsphere therein; first, at 900 C. and thereafter at 1100 C. Time measurements at the lower, or sintering, temperature were made after the compact reached the sintering temperature. The time at the higher temperature was measured when the sintered material entered that zone.

Tensile strength measurements for each of the specimens prepared were obtained using a universal tester by measuring the breaking load (kg/mm?) of the specimens. The elongation (in percent) was also measured. The compositions shown are all in weight percent.

Further, specimens prepared in accordance with the present invention and designated as A were compared against specimens made in accordance with conventional process and designated as B, after physical test measurements using the above-described procedure were per formed. The results are included in the examples shown below, as Well as in the summary Table I.

EXAMPLE 1 A compact of iron powder and 2% copper powder admixed was formed and sintered at 900 C. for 60 minutes and thereafter heated at 1100 C. for 16 minutes in accordance with the method of this invention. Specimen A1, prepared therefrom, was tested; the tensile strength measured 26 kg./mm. and the elongation was 8%.

In comparison, a compact formed of the same iron- 2% copper admixture was completely heat treated at 1100 C. for 60 minutes, in accordance with the conventional method. Specimen B1 prepared therefrom was tested; the tensile strength measured 26 kg./mm. and the elongation was 5%.

EXAMPLE 2 A compact formed from an admixture of iron powder and 5% copper powder was sintered at 900 C. for 60 minutes and thereafter heated at 1100 C. for 30 minutes, in accordance with the method of this invention. Specimen A2 prepared therefrom was tested; the tensile strength measured 31 kg./mm. and the elongation was 5%.

In comparison, a campact formed of the same iron- 5% copper admixture was completely heat treated at 1100 C. for minutes, in accordance with the conventional method. Specimen B2 prepared therefrom was tested; the tensile strength measured 33 kg./mm. and the elongation was 2.5%.

EXAMPLE 3 A compact formed from an admixture of iron powder and 2% copper powder was sintered at 900 C. for 30 minutes, repressed under a pressure of 7 t./cm. and thereafter heated at 1100 C. for 15 minutes, in accordance with the method of this invention. Specimens A3 prepared therefrom was tested; the tensile strength measured 34 kg/mm. and the elongation was 17%.

In comparison, a compact formed of the same iron- 2% copper admixture was sintered at 1100 C. for 30 minutes, repressed under a pressure of 7 t./cm. and thereafter heated at 1100 C. for 30 minutes, using the conventional method. Specimen B3 prepared therefrom was tested; the tensile strength measured 34 kg./mm. and the elongation was 8%.

EXAMPLE 4 A compact formed of an admixture of metal powders, that is, iron powder with 2% nickel powder and 2% copper powder was sintered at 900 C. for 60 minutes and thereafter heated at 1100 C. for 30 minutes, in accordance with the method of this invention. Specimen A4 prepared therefrom was tested; the tensile strength measured 30 kg./mm. and the elongation was 10%.

In comparison, a compact formed of the same iron- 2% nickel-2% copper admixture was sintered at 1100 C. for 30 minutes, representing the full treatment under the conventional method. Specimen B4 prepared therefrom was tested; the tensile strength measured 30 kg./mm. and the elongation was 4%.

EXAMPLE 5 A compact formed from iron powder alone was sintered at 1100 C. for 60 minutes and thereafter the sintered compact was contacted against copper and heated, whereby molten copper was infiltrated into the pore structure at 1100 C. for 30 minutes, in accordance with the method of this invention. Specimen A5 prepared therefrom was tested; the tensile strength measured 48 kg./mm. and the elongation was 12%.

In comparison, a compact was also formed from iron powder alone and was sintered and simultaneously impregnated with molten copper at 1100 C. for 60 minutes, in accordance with the conventional method. Specimen B5 prepared therefrom, was tested; the tensile strength measured 56 kg./mm. and the elongation was 3.5%.

EXAMPLE 6 A compact formed from an iron powder, 0.2% carbon powder admixture was sintered at 1100 C. for 60 minutes and thereafter the sintered compact was contacted against copper and heated, whereby molten copper was infiltrated into the pore structure at 1100 C. for 30 minutes, in accordance with the method of this invention. Specimen A6 prepared therefrom was tested; the tensile strength measured 50 kg./mm. and the elongation was 8%.

In comparison, a compact formed of the same iron- 0.2% carbon mixture was sintered and simultaneously impregnated with molten copper at 1100 C. for 60 minutes, in accordance with the conventional method. Specimen B6 prepared therefrom was tested; the tensile strength measured 60 kg./mm. and the elongation was 1%.

Table I, shown below, summarizes the results of the foregoing examples; A represents specimens made in accordance with the present invention, and B represents specimens made in accordance with conventional methods:

From the foregoing examples, the results of which are summarized in Table I, it will be apparent that significant improvements in the toughness of the iron base sintered alloy structure is realized when the present invention is employed over those sintered materials prepared using conventional methods. Iron base sintered alloys are produced with tensile strengths equal to the best conventional sintered alloys, but with elongation values ranging from 50% to 800% higher than those previously produced.

While preferred embodiments of the iron base sintered alloy containing copper have been disclosed in the foregoing description, it should be understood that various modifications within the spirit of the invention may occur to those skilled in the art.

We claim:

1. A method for producing tough, as-formed, sintered alloy materials comprising the steps of (1) uniformly mixing iron powder with up to 8% by weight of copper,

(2) forming an iron-base compact from said admixture of step (1),

(3) heating said compact at a temperature ranging from 700 C. to 1000 C. for less than minutes to form a network of sintered iron,

(4) heating said sintered compact at a temperature ranging from 1100 C. to 1500 C. for a period of time between 4 minutes to 30 minutes so that the copper in said compact is melted and diffused in said iron non-uniformly.

2. A method in accordance with claim 1, wherein said admixture additionally includes, by weight, up to 2% nickel powder or up to 2% carbon powder.

3. A method in accordance with claim 1, wherein said sintered compact is repressed prior to being heated for diffusion purposes.

References Cited UNITED STATES PATENTS 2,633,628 4/1953 Bartlett 29l82.l 3,494,747 2/1970 Burr 29-1821 3,352,647 11/1967 MacDonald et al. 29182.1 3,459,547 8/ 1969 Andreotti et a1 29182.l 2,456,779 12/1948 Goetzel 148126 3,498,763 3/1970 Savage -208 CARL D. QUAR'FORTH, Primary Examiner B. H. HUNT, Assistant Examiner U.S. Cl. X.R. 

